java9新特性

1.模块就是代码和数据的封装体。模块的代码被组织成多个包，每个包中包含Java类和接口；模块的数据则包括资源文件和其他静态信息。 跳过..
 2.REPL (JShell) 类似python的交互式 跳过 .... 
3.改进的 Javadoc 跳过... 
4.多版本兼容 JAR 包 跳过.. 
5.集合工厂方法

　　旧方法创建集合

import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
 
public class Tester {
   public static void main(String []args) {
      Set<String> set = new HashSet<>();
      set.add("A");
      set.add("B");
      set.add("C");
      set = Collections.unmodifiableSet(set);
      System.out.println(set);
      List<String> list = new ArrayList<>();
 
      list.add("A");
      list.add("B");
      list.add("C");
      list = Collections.unmodifiableList(list);
      System.out.println(list);
      Map<String, String> map = new HashMap<>();
 
      map.put("A","Apple");
      map.put("B","Boy");
      map.put("C","Cat");
      map = Collections.unmodifiableMap(map);
      System.out.println(map);
   }
}

[A, B, C]
[A, B, C]
{A=Apple, B=Boy, C=Cat}


Java 9 中，以下方法被添加到 List，Set 和 Map 接口以及它们的重载对象。

static <E> List<E> of(E e1, E e2, E e3);
static <E> Set<E>  of(E e1, E e2, E e3);
static <K,V> Map<K,V> of(K k1, V v1, K k2, V v2, K k3, V v3);
static <K,V> Map<K,V> ofEntries(Map.Entry<? extends K,? extends V>... entries)


import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.AbstractMap;
import java.util.Map;
import java.util.Set;
 
public class Tester {
 
   public static void main(String []args) {
      Set<String> set = Set.of("A", "B", "C");      
      System.out.println(set);
      List<String> list = List.of("A", "B", "C");
      System.out.println(list);
      Map<String, String> map = Map.of("A","Apple","B","Boy","C","Cat");
      System.out.println(map);
  
      Map<String, String> map1 = Map.ofEntries (
         new AbstractMap.SimpleEntry<>("A","Apple"),
         new AbstractMap.SimpleEntry<>("B","Boy"),
         new AbstractMap.SimpleEntry<>("C","Cat"));
      System.out.println(map1);
   }
}



[A, B, C]
[A, B, C]
{A=Apple, B=Boy, C=Cat}
{A=Apple, B=Boy, C=Cat}

　6.接口中可以有私有方法

public class Tester {
   public static void main(String []args) {
      LogOracle log = new LogOracle();
      log.logInfo("");
      log.logWarn("");
      log.logError("");
      log.logFatal("");
      
      LogMySql log1 = new LogMySql();
      log1.logInfo("");
      log1.logWarn("");
      log1.logError("");
      log1.logFatal("");
   }
}
final class LogOracle implements Logging { 
}
final class LogMySql implements Logging { 
}
interface Logging {
   String ORACLE = "Oracle_Database";
   String MYSQL = "MySql_Database";
 
   private void log(String message, String prefix) {
      getConnection();
      System.out.println("Log Message : " + prefix);
      closeConnection();
   }
   default void logInfo(String message) {
      log(message, "INFO");
   }
   default void logWarn(String message) {
      log(message, "WARN");
   }
   default void logError(String message) {
      log(message, "ERROR");
   }
   default void logFatal(String message) {
      log(message, "FATAL");
   }
   private static void getConnection() {
      System.out.println("Open Database connection");
   }
   private static void closeConnection() {
      System.out.println("Close Database connection");
   }
}




以上实例执行输出结果为：
Open Database connection
Log Message : INFO
Close Database connection
Open Database connection
Log Message : WARN
Close Database connection
Open Database connection
Log Message : ERROR
Close Database connection
Open Database connection
Log Message : FATAL
Close Database connection

标签：Map,java,String,Database,特性,util,import,java9
来源： https://www.cnblogs.com/q1359720840/p/10990885.html